Mixers are normally used in radio transmitter or receiver circuits for frequency translation of signals between different frequency bands, such as basebands, intermediate frequency (IF) bands, and radio frequency (RF) bands.
In order to facilitate wireless communication at increasing data rates, various new standards and systems for mobile communication are emerging. Specifications for fourth generation (4G) mobile communication systems are being drawn up under IMT (International Mobile Telecommunication) Advanced. Future communication systems to be compliant with IMT Advanced require relatively wide RF (Radio Frequency) frequency bands, e.g. to accommodate relatively high bit rates. A problem that has been identified for communication systems compliant with IMT Advanced is that there is normally a lack of sufficiently wide free RF frequency bands; most frequency bands are fragmented, e.g. with different parts of a band being licensed for usage by different operators etc. Continuous frequency bands of e.g. 100 MHz bandwidth or more are normally not available. One way to address this problem is to set up a transmission link between a base station and mobile terminal using several sub bands that are scattered across a total frequency bandwidth to form an aggregated spectrum.
An example of an emerging cellular system is 3G Long Term Evolution (3G LTE). In 3G LTE, signals are transmitted using OFDM (Orthogonal Frequency Division Multiplexing) in a multiple access technique referred to as OFDMA (Orthogonal Frequency Division Multiple Access) in the downlink from a base station to a mobile terminal. Different groups of subcarriers, commonly referred to as resource blocks (RBs), of OFDM symbols transmitted from the base station can be allocated to different mobile terminals, whereby multiple access is obtained.
For the examples mentioned above, the frequency band or bands allocated to a particular mobile terminal are normally not fixed, but may vary over time within a relatively large range of possible frequency bands. Relatively hard requirements may be set on mixer arrangements used for frequency translation in transmitters and/or receivers, e.g. in terms of suppression of harmonics of local oscillator (LO) signals.
WO 2009/057051 discloses an electronic device comprising a passive harmonic-rejection mixer. The passive harmonic rejection mixer has an input connected to several sub-mixer stages, and the sub-mixer stages are connected to a summing module for generating the output. Each sub-mixing stage comprises a gating module and a respective amplifier, the gating module adapted to selectively pass the input signal or the input signal with inverted polarity under the control of control signals.